RE scientists have several models that explain gravity quite nicely.

If there are several models then it really isn't explained at all, is it?

No. More than often in the real world, finding the relationship between two variables (say, Force and mass) is a complicated function that we can't seem to describe very clearly. This is where piecewise functions come in. You can restrict the variable of mass to be between certain values, and then it'll be easy to fit a simple function in to describe it. For example, for values much less than the speed of light, F=ma describes this relationship very well.